The present invention relates to a recording liquid and an image recording method, and more particularly to a recording liquid comprising a colorant, water and fine resin particles, and an image recording method using the same.
Recently, attentions have been paid to ink jet systems, i.e., image recording methods in which droplets of recording liquids are discharged from recording heads to record images on recording media, because the running cost thereof is low and this system can be easily applied to color image system for output devices of information instruments such as computers. As recording liquids for ink jet printers, aqueous solutions of dyes which are mainly composed of water and dyes have hitherto been used. However, there is the problem that when recording liquids jetted from nozzles adhere to recording paper, they blurred on the recording paper so that the resulting dot images become extremely larger droplets formed by jetting, or have low image density, to thereby result in low image quality. Further, there is the problem that the images are easily blurred or flow with water, because of low water resistance of the recorded images. Furthermore, there is the problem that the images are easily faded by irradiation of light such as sunlight, because of low light resistance.
As to recording liquids for ink jet printers, techniques have been proposed in which film-forming fine resin particles are added to recording liquids to solve the above described problems of the aqueous solutions of dyes. For example, JP-B-60-32663 (the term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d) discloses a recording liquid to which a latex is added as the fine resin particles, JP-A-5-239392 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent application) discloses a recording liquid to which a water-dispersible resin having carboxyl and nonionic hydrophilic groups is added, JP-A-5-255628 discloses a recording liquid to which a vinyl polymer of a non-crosslinked structure, and JP-A-6-340835 discloses a recording liquid to which polyester particles having ionic groups are added. Further, JP-B-7-47355 discloses a technique which comprises adding particles of a resin such as a polyester and a crosslinking agent to a recording liquid, and crosslinking the resin on a recording medium.
However, in all of the recording liquids disclosed in the above described patents, film formation of the fine resin particles is initiated at discharge outlet sections of recording heads as water contained in the recording liquids is evaporated by contacting with air. This results in occurrence of clogging. It has been therefore impossible to stably discharge the recording liquids. Further, according to these recording liquids, it has been impossible to completely prevent the recording liquids from blurring in fibers of recording paper by capillary action, to thereby fail to provide images of high image quality. Furthermore, it has been impossible to completely prevent these recording liquids from penetrating into the inside of the recording paper, which imposes a limitation on the acquisition of images of high density and high image quality. Similarly, there is also a limitation on water resistance. Moreover, the dilution of the above described conventional recording liquids with water for avoiding the clogging at discharge outlets decreases the content of fine resin particles contained in the same volume of droplets, namely the content of resin solids contributing to image formation, as compared to that prior to the dilution, which causes a remarkable reduction in image density. It has been therefore impossible to provide images of high image quality. That is, in the conventional recording liquids, the provision of images having a high image density and high image quality by increasing the content of fine resin particles (the content of resin solids) has been incompatible with the avoidance of the clogging at discharge outlets.
The present invention has been made for solving the above described problems, and an object of the present invention is to provide a recording liquid which can provide an image having a high image density, exhibiting no blurring on recording paper and no penetration therein, and having excellent water resistance, and which is excellent in discharge stability.
Another object of the present invention is to provide an image recording method using the recording liquid.
Other objects and effects of the present invention will become apparent from the following description.
The above described objects of the present invention has been achieved by providing a recording liquid comprising a colorant, water and at least two kinds of fine resin particles.
In a first preferred embodiment, the recording liquid comprises a colorant, water and at least two kinds of fine resin particles, wherein at least one kind of the at least two kinds of fine resin particles are fine self-crosslinkable resin particles.
In a second preferred embodiment, the recording liquid comprises a colorant, water and at least three kinds of fine resin particles.
The present invention also relates to an image recording method comprising discharging droplets of the above described recording liquid from a recording head to record an image on a recording medium.
The reason why the recording liquids as described above allows the attainment of high image density by increasing the content of fine resin particles (the content of resin solids) to be compatible with the avoidance of the clogging at a discharge outlet of a recording head is not fully clarified, but inferred as follows.
The inclusion of at least two different kinds of fine resin particles in the recording liquid decreases the probability that around (at proximate coordinate positions) a certain fine resin particle is present a fine resin particle of the same kind as this fine resin particle. This decreases the probability that the fine resin particles of the same kind come close to and collide with each other, which inhibits a series of processes from the approach of the fine resin particles of the same kind to each other to film formation through their collision and fusion (coordination effect), resulting in prevention of clogging.
Similarly, the inclusion of at least three different kinds of fine resin particles in the recording liquid decreases the probability that around (at proximate coordinate positions) a certain fine resin particle is present a fine resin particle of the same kind as the fine resin particle to one third or less. This decreases the probability that the fine resin particles of the same kind come close to and collide with each other, which inhibits a series of processes from the approach of the fine resin particles of the same kind to each other to film formation through their collision and fusion (coordination effect), resulting in prevention of clogging.
Further, the attraction between particles becomes more difficult to act when different kinds of fine resin particles are present in the recording liquid than when only fine resin particles of the same kind are present (the repulsion becomes easy to act). Accordingly, fine resin particles of the same kind are prevented from coming close to each other, and the probability of their collision is decreased (the effect of repulsion between particles). Similar to the above, therefore, a series of processes from the approach of the fine resin particles of the same kind to each other to film formation through their collision and fusion is inhibited, resulting in prevention of the clogging.
Furthermore, with respect to the prevention of the clogging, it is considered that the differences in particle size and form between the different kinds of fine resin particles are larger than those between the fine resin particles of the same kind. When around a certain fine resin particle is present a different kind of fine resin particle largely different therefrom in particle size and form, the fine resin particles of the same kind and the different kinds are prevented from coming close to each other (geometrical structure effect), thereby also possibly preventing the clogging as similar to the above.
In the present invention, the fine resin particles are remarkably prevented from coming close to each other by the sum of the above described effects, so that the total content of the fine resin particles contained in the recording liquid can be increased. The content of the fine resin particles in one droplet can also be increased as well which makes it possible to form images of high image density.
In addition, images can be rapidly formed on the recording paper by the high-speed film-forming property of fine self-crosslinkable resin particles contained in the recording liquid. That is, the crosslinking reaction of the fine self-crosslinkable resin particles proceeds at high speed with evaporation of water contained in droplets of the recording liquid and penetration of the recording liquid in the paper from immediately after adhesion of the droplets of the recording liquid jetted from the recording head to the recording paper, thereby rapidly forming a firm image film in which the colorant is enclosed in the resin. At this time, in the first preferred embodiment, the film formation of other coexistent fine self-crosslinkable resin particles and fine resin particles other than the fine self-crosslinkable resin particles also proceeds. In the second preferred embodiment, the film formation of the three or more kinds of fine resin particles proceeds side by side. This prevents the recording liquid from blurring and penetrating. Thus, it becomes possible to form images comprising resins and a colorant enclosed therein, and having a high image density and high water resistance, on the recording medium such as paper.
The present invention is described in detail below.
The recording liquid of the first preferred embodiment of the present invention comprises a colorant, water and at least two kinds of fine resin particles in which fine resin particles of at least one kind are fine self-crosslinkable resin particles.
The term xe2x80x9cself-crosslinkable resinxe2x80x9d as used in the present invention means a resin which crosslinks by the reactivity of functional groups incorporated into a main chain and/or side chains of the resin, not by the action of a crosslinking agent. Examples of such fine self-crosslinkable resin particles include fine acrylsilicone resin particles and fine acrylamide resin particles. Of these, fine acrylsilicone resin particles containing an alkoxysilyl group are preferred which can rapidly form firm siloxane crosslinked films with colorants enclosed therein, from the viewpoints of the high-speed film-forming property suitable for rapid image formation and the strength of the formed films. In the alkoxysilyl group of the fine alkoxysilyl group-containing acrylsilicone resin particles, the alkyl group is preferably alkyl having 1 to 3 carbon atoms, and more preferably alkyl having 1 or 2 carbon atoms. The acrylic skeletons include, for example, polymers and copolymers of styrene, vinyltoluene, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, vinyl acetate, acrylonitrile, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methacrylic acid, acrylic acid, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, 2-hydroxyethyl acrylate, acrylamide, N-methylolacrylamide and glycidyl methacrylate.
The fine resin particles which can be used together with the above described fine self-crosslinkable resin particles include fine non-crosslinkable resin particles and fine resin particles crosslinkable by the action of crosslinking agents. Specifically, they include fine fluororesin particles, fine acrylic resin particles, fine polyester resin particles, fine vinyl acetate resin particles, fine vinyl chloride resin particles, fine styrene-butadiene copolymer resin particles, fine polyurethane resin particles, fine polystyrene resin particles, fine vinyl acetate-acrylic copolymer resin particles, vinyl acetate-acrylamide copolymer resin particles, ethylene-vinyl acetate copolymer resin particles, fine epoxy resin particles, fine polyamide resin particles and fine silicone resin particles.
In this embodiment, the fine resin particles contained in the recording liquids may be composed of the fine self-crosslinkable resin particles, or the fine self-crosslinkable resin particles and the fine non-crosslinkable resin particles and/or the fine resin particles crosslinkable by the action of crosslinking agents. However, the fine resin particles are preferably composed of the fine self-crosslinkable resin particles and the fine non-crosslinkable resin particles, from the viewpoint of making it difficult to form films by the time difference between film formation processes of the respective resins and by the composition difference, to thereby prevent clogging, namely, film formation at discharge outlets of recording heads. Of the fine non-crosslinkable resin particles enumerated, fine fluororesin particles are preferred, because they are excellent in the film-forming property (image forming property), have high water repellency, high water resistance and high weather resistance, and are useful for forming images having high water resistance and a high image density. As the fine fluororesin particles, fine fluororesin particles having fluoroolefin units are preferred. Fine fluorine-containing vinyl ether resin particles composed of fluoroolefin units and vinyl ether units are particularly preferred among others.
Examples of the fluoroolefin units include xe2x80x94CF2CF2xe2x80x94, xe2x80x94CF2CF(CF3)xe2x80x94 and xe2x80x94CF2CFClxe2x80x94. On the other hand, examples of the vinyl ether units include those shown below. 
As the fine fluorine-containing vinyl ether resin particles composed of fluoroolefin units and vinyl ether units, alternating copolymers are preferred in which the above described fluoroolefin units and vinyl ether units are alternately combined.
The recording liquid according to the first preferred embodiment of the present invention contains at least two kinds of fine resin particles including fine self-crosslinkable resin particles. This sufficiently allows the attainment of high image density and high image quality by the increase of the resin solids content to be compatible with the avoidance of clogging. However, when the recording liquid contains three or more kinds of fine resin particles including fine self-crosslinkable resin particles, the above described probability that fine resin particles of the same kind are present at proximate coordinate positions is further decreased (enhancement of the coordination effect), and the attraction between particles becomes more difficult to act. Accordingly, the clogging can be more effectively prevented. There is no particular limitation on the upper limit with respect to the number of the kinds of fine resin particles contained in the recording liquid. However, when it is assumed that the shape and size of each fine resin particle are constant and that the shape is spherical, the proximate particle number (coordinate number) in the state where the particles are filled most densely, namely the number of particles existing in contact with a certain particle, amounts 12. Accordingly, the optimum value of the upper limit number of the kinds of fine resin particles is considered to be 12. Further considering the width of probabilistic deviation, the upper limit number of the kinds of fine resin particles is preferably 18 (12 kinds +6 kinds). From the above, the number of the kinds of fine resin particles contained in the recording liquid according to the first preferred embodiment of the present invention is preferably 2 to 18, and more preferably 3 to 12, from the viewpoints of the approach of the fine resin particles of the same kind to each other by the coordination effect and a decrease in collision probability. In the present invention, fine resin particles different in at least one of the characteristics of the fine resin particles or a dispersion thereof, namely, lowest film-forming temperature, glass transition temperature, ionicity, pH, weight average molecular weight and average particle size, caused by the difference in a modifying method, are considered to fine resin particles of another kind, even if the resin is composed of the same monomer.
The average particle size of the respective fine resin particles for use in the first preferred embodiment of the present invention is preferably 0.01 xcexcm to 5 xcexcm, and more preferably 0.05 xcexcm to 3 xcexcm. The fine resin particles having an average particle size of less than 0.01 xcexcm are deteriorated in the film-forming property, whereas exceeding 5 xcexcm results in lowered optical density (image density).
In the first preferred embodiment of the present invention, the total content of the fine resin particles (the total of the resin solid content) is preferably 10 to 95% by weight, more preferably 15 to 90% by weight, and most preferably 20 to 80% by weight, based on the weight of the recording liquid. The fine resin particles having a total content of less than 10% by weight are lowered in image optical density, whereas exceeding 95% by weight raises a fear of lowered discharge stability. Further, when two kinds of fine resin particles are used, the content of the fine self-crosslinkable resin particles contained in the recording liquid preferably ranges from 0.05 W parts by weight to 0.9 W parts by weight, taking the total solid content of the fine resin particles as W parts by weight. Furthermore, when three or more kinds of fine resin particles are used, the content of the respective fine resin particles contained in the recording liquid can be appropriately selected so as to realize desired characteristics at maximum. When n kinds (n: a positive integer of 3 or more) of fine resin particles are mixed, the solid content of the respective fine resin particles contained in the recording liquid is preferably within the range of 0.1 W/n parts by weight to 2 W/n parts by weight, taking the total solid content of the fine resin particles contained in the recording liquid as W parts by weight. If the content is less or more than this range, the effect of preventing the clogging by coexistence of two or more different kinds of fine resin particles may be reduced. Furthermore, of the fine resin particles contained in the recording liquid, the content of the fine self-crosslinkable resin particles is preferably within the range of 0.1 W/n parts by weight to 2 W/n parts by weight as similar to the above, and more preferably 0.4 W/n parts by weight to 2 W/n parts by weight, per one kind thereof. If the content is more than 2 W/n parts by weight, the effect of preventing the clogging by coexistence of two or more different kinds of fine resin particles is reduced as described above. On the other hand, if the content is less than 0.4 W/n parts by weight, the image formation speed on paper is decreased to arise a fear of lowered image density.
In the second preferred embodiment, the recording liquid of the present invention comprises a colorant, water and at least three kinds of fine resin particles.
The fine resin particles for use in the second embodiment of the present invention include fine non-crosslinkable resin particles, fine self-crosslinkable resin particles and fine resin particles crosslinkable by the action of crosslinking agents. Specifically, fine resin particles such as fine fluorine resin particles, fine polyester resin particles, fine vinyl acetate resin particles, fine vinyl chloride resin particles, fine styrene-butadiene copolymer resin particles, fine polyurethane resin particles, fine polystyrene resin particles, fine vinyl acetate-acrylic copolymer resin particles, vinyl acetate-acrylamide copolymer resin particles, ethylene-vinyl acetate copolymer resin particles, fine epoxy resin particles, fine polyamide resin particles, fine silicone resin particles, fine acrylic resin particles and fine acrylsilicone resin particles can be used. The term xe2x80x9cself-crosslinkable resinxe2x80x9d as used in the present invention means a resin which crosslinks by the reactivity of functional groups incorporated into a main chain and/or side chains of the resin, not by the action of a crosslinking agent.
In the second embodiment of the present invention, of the three or more kinds of fine resin particles contained in the recording liquid, at least one kind of fine resin particles are preferably the fine non-crosslinkable resin particles, from the viewpoint of making it difficult to form films by the time difference between film formation processes of the respective resins and by the composition difference, to thereby prevent clogging, namely, film formation at discharge outlets of recording heads. Of the fine non-crosslinkable resin particles enumerated, fine fluorine resin particles are preferred, because they are excellent in the film-forming property (image forming property), have high water repellency, high water resistance and high weather resistance, and are useful for forming images having high water resistance and a high image density. As the fine fluororesin particles, fine fluororesin particles having fluoroolefin units are preferred. Fine fluorine-containing vinyl ether resin particles composed of fluoroolefin units and vinyl ether units are particularly preferred among others.
Examples of the fluoroolefin units include xe2x80x94CF2CF2xe2x80x94, xe2x80x94CF2CF(CF3)xe2x80x94 and xe2x80x94CF2CFClxe2x80x94. On the other hand, examples of the vinyl ether units include those shown below: 
As the fine fluorine-containing vinyl ether resin particles composed of fluoroolefin units and vinyl ether units alternating copolymers are preferred in which the above described fluoroolefin units and vinyl ether units are alternately combined.
The recording liquid according to the second preferred embodiment of the present invention contains at least three kinds of fine resin particles. This sufficiently allows the attainment of high image density and high image quality by the increase of the content of resin solids to be compatible with the avoidance of clogging. However, when the recording liquid contains four or more kinds of fine resin. particles, the probability that fine resin particles of the same kind are present at the above described proximate coordinate positions is further decreased (enhancement of the coordination effect), and the attraction between particles becomes more difficult to act. Accordingly, the clogging can be more effectively prevented. There is no particular limitation on the upper limit with respect to the number of the kinds of fine resin particles contained in the recording liquid. However, when it is assumed that the shape and size of each fine resin particle are constant and that the shape is spherical, the proximate particle number (coordinate number) in the state where the particles are filled most densely, namely the number of particles existing in contact with a certain particle, amounts 12. Accordingly, the optimum value of the upper limit number of the kinds of fine resin particles is considered to be 12. Further considering the width of probabilistic deviation, the upper limit number of the kinds of fine resin particles is preferably 18 (12 kinds+6 kinds). From the above, the number of the kinds of fine resin particles contained in the recording liquid according to the second preferred embodiment of the present invention is preferably 3 to 18, and more preferably 4 to 12, from the viewpoints of the approach of the fine resin particles of the same kind to each other by the coordination effect and a decrease in collision probability. In the present invention, fine resin particles different in at least one of the characteristics of the fine resin particles or a dispersion thereof, namely, lowest film-forming temperature, glass transition temperature, ionicity, pH, weight average molecular weight and average particle size, caused by the difference in a modifying method, are considered to fine resin particles of another kind, even if the resin is composed of the same monomer.
The average particle size of the respective fine resin particles for use in the second preferred embodiment of the present invention is preferably 0.01 xcexcm to 5 xcexcm, and more preferably 0.05 xcexcm to 3 xcexcm. The fine resin particles having an average particle size of less than 0.01 xcexcm are deteriorated in the film-forming property, whereas exceeding 5 xcexcm results in lowered optical density (image density).
In the second preferred embodiment of the present invention, the total content of the fine resin particles (the total of the resin solid content) is preferably 10 to 95% by weight, more preferably 15 to 90% by weight, and most preferably 20 to 80% by weight, based on the weight of the recording liquid. The fine resin particles having a total content of less than 10% by weight are lowered in image optical density, whereas exceeding 95% by weight raises a fear of lowered discharge stability. Further, the content of the respective fine resin particles contained in the recording liquid can be appropriately selected so as to realize desired characteristics at maximum. When n kinds (n: a positive integer of 3 or more) of fine resin particles are mixed, the solid content of the respective fine resin particles contained in the recording liquid is preferably within the range of 0.1 W/n parts by weight to 2 W/n parts by weight, taking the total solid content of the fine resin particles contained in the recording liquid as W parts by weight. If the content is less or more than this range, the effect of preventing clogging by coexistence of three or more different kinds of fine resin particles may be reduced. Further, of the fine resin particles contained in the recording liquid, the content of the fine non-crosslinkable resin particles is preferably within the range of 0.1 W/n parts by weight to 2 W/n parts by weight as similar to the above, and more preferably 0.3 W/n parts by weight to 2 W/n parts by weight, per one kind thereof. If the content is more than 2 W/n parts by weight, the effect of preventing clogging by coexistence of three or more different kinds of fine resin particles is reduced as described above. On the other hand, if the content is less than 0.3 W/n parts by weight, there is a fear of reduced water resistance, as well as lowered clogging prevention effect.
In the present invention, the colorant preferably has a good affinity for water, i.e., a main solvent in the recording liquids of the present invention, or has a good uniform dispersibility. Specifically, pigments, water-soluble dyes and disperse dyes are used.
The pigments for use in the present invention include organic dyes and inorganic dyes. Examples of the pigments for black-and-white images include carbon black (C. I. Pigment Black 7) such as furnace black and channel black, and organic pigments such as aniline black (C. I. Pigment Black 1). Further, the pigments for color images include pigments such as C. I. Pigment Yellows 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42, 53, 55, 81, 83, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 138 and 153, C. I. Pigment Violets 1, 3, 5:1, 16, 19, 23 and 38, and C. I. Pigment Blues 1, 2, 15, 15:1, 15:2, 15:3, 15:4, 15:6 and 16. The content of the pigments contained in the recording liquid is preferably 1 to 50% by weight, and more preferably 1.5 to 40% by weight. In order to disperse these pigments more uniformly, they may be dispersed in a ball mill or the like as needed.
The water-soluble dyes for use in the present invention include direct dyes and acid dyes. Examples thereof include, but are not limited to, C. I. Direct Blacks 9, 17, 19, 22, 32, 51, 56, 62, 69, 77, 80, 91, 94, 97, 108, 112, 113, 114, 117, 118, 121, 122, 125, 132, 146, 154, 166, 168, 173 and 199, C. I. Direct Violets 7, 9, 47, 48, 51, 66, 90, 93, 94, 95, 98, 100 and 101, C. I. Direct Yellows 8, 9, 11, 12, 27, 28, 29, 33, 35, 39, 41, 44, 50, 53, 58, 59, 68, 86, 87, 93, 95, 96, 98, 100, 106, 108, 109, 110, 130, 132, 144, 161 and 163, C. I. Direct Blues 1, 10, 15, 22, 25, 55, 67, 68, 71, 76, 77, 78, 80, 84, 86, 87, 90, 98, 106, 201, 202, 244, 251 and 280, C. I. Acid Blacks 7, 24, 29 and 48, C. I. Acid Violets 5, 34, 43, 47, 48, 90 and 103, C. I. Acid Yellows 17, 19, 23, 25, 39, 40, 44, 49, 50, 61, 110, 174 and 218, and C. I. Acid Blues 9, 25, 40, 41, 62, 72, 76, 80, 106, 112, 120, 205, 230, 271 and 280. The content of these dyes contained in the recording liquid is determined depending on the kind of dye, the kind of solvent component, characteristics required for the recording liquid, and the like. In general, however, it is preferably within the range of 0.2 to 40% by weight, and more preferably within the range of 0.5 to 30% by weight based on the weight of the recording liquid.
Preferred examples of water used in the present invention include ion-exchanged water, ultrapure water, distilled water and ultrafiltrated water.
In addition, pH adjustors such as potassium dihydrogenphosphate and sodium dihydrogenphosphate, and benzoic acid, dichlorophene, hexachlorophene and sorbic acid for antifungal, preservative and rust preventive purposes may be added to the recording liquid as needed. Furthermore, various general additives such as ethylene glycol and glycerine may be added to the recording liquid as needed.
The recording liquid of the present invention can be used in an image recording method comprising discharging droplets of the recording liquid from a recording head to record an image on a recording medium.
Further, the recording liquid of the present invention can be appropriately used not only for the above described ink jet recording, but also for image recording of the electrostatic attraction system and writing things.
The present invention will be described in more detail below with reference to the following Examples, but the invention should not be construed as being limited thereto.